Increased bronchial reactivity to various aerosol challenges, including histamine, has been shown to be present in patients with chronic bronchitis. A further increase in bronchial reactivity during respiratory infections has also been shown. The present project proposes to study asymptomatic cigarette smokers with and without peripheral airway disease, by delivering sub-micronic aerosols of histamine before during and after acute viral respiratory infections in order to test whether increased reactivity relates to the presence of peripheral airway disease and to acute viral infections. Frequency dependence of compliance, closing volumes, resistance and maximal expiratory flow volume curves with air and 80% helium-20% oxygen will be measured.